Optimal Selection Of Ultrasonic Phased Array Probe For Heavy-walled CCASS Pipe Welds Inspection

Ultrasonic phased array technology provides a new solution for the non-destructive testing of heavy-walled centrifugal casting austenitic stainless steel (CCASS) pipeline welds, and the appropriate choice of phased array probe is an extremely important premise to improve the detection effect. In this paper, theoretical analysis, numerical simulation combined with the actual test were used and from the aspects of probe type, wave type, frequency, and aperture to choose phased array probes for the detection of heavy-walled CCASS pipe welds.To analyse the metallographic photos of CCASS pipe welds block:obvious hierarchical layers and coarse grains were found; utilized conventional0.5MHz,1MHz,2MHz ultrasound probe to measure its attenuation coefficient, signal to noise ratio and main frequency offsets of bottom echo, the results showed that:ultrasound is intensely attenuated and severe noise appeared; attenuation coefficient increases with the testing frequency, and the signal to noise ratio is reduced accordingly. By testing different regions of the specimen and processing the signal, results showed that:the main frequency offset of bottom echo of0.5MHz is small and relatively uniform, main frequency offset of2MHz is larger and fluctuated significantly,1MHz is in the middle, that was to say high frequency is more sensitive to the heterogeneity of CCASS material, so testing frequency for the CCASS pipe welds should be less than2MHz.Utilized0.75MHz and1MHz two-dimensional phased array TRL (transmit/receive longitudinal) probes to test the side-drilled holes on CCASS pipe welds test block whose depth was16mm,32mm,48mm, and diameter was3mm, then compared the beam energy, signal to noise ratio, lateral resolution and axial resolution. The results showed that: to shallow area of the CCASS,1MHz Phased array probe has better axial resolution and signal to noise ratio than0.75MHz probe; correspond to deeper areas, the acoustic dispersion of1MHz is greater than0.75MHz probe, side-drilled hole imagings distortes and signal to noise ratio is lower.The Ultravision software was used to simulate the sound field characteristics under different elements combination of0.75MHz two-dimensional phased array TRL probe, which were the front six groups, middle six groups, middle eight groups, whole10groups and the end six groups, then combined with experiments to measure the beam energy, signal to noise ratio, lateral resolution of side-drilled holes on the CCASS specimen, the results showed that: to shallow area of the CCASS, it is better to use the end six groups which has a higher position on the wedge; to the deeper region, in order to ensure the beam energy and detection resolution, it is desirable to use all10groups elements.Used a scanner to carry0.75MHz and1MHz two-dimensional phased array TRL probe to scan the side-drilled holes on carbon steel specimen whose diameter was3mm, depth was25mm,50mm,75mm; the side-drilled holes on CCASS specimen whose diameter was3mm,4.8mm, depth was16mm,32mm,48mm; the simulated cracks on CCASS specimen whose width was1mm, height was4%,5%,7.5%,10%and12%wall thickness, results showed that: all defects were detected, the positioning error of defects on the carbon steel is0.1-1mm, the positioning error of defects on the CCASS block is0.1-2.6mm.